Question

Please help:

g++ (GCC) 3.4.4

I have two ‘.hpp’ files: ‘UnionFind.hpp’ and “Graph.hpp”. The content of the files is as follows:

#ifndef UNIONFIND_HPP
#define UNIONFIND_HPP

#include <vector>

using std::vector;

class UnionFind
{
   public:
      UnionFind(uint32_t size);
      ~UnionFind();
      int find(uint32_t target);
      void join(uint32_t a, uint32_t b);
      void print();
   private:
      uint32_t size;
      uint32_t* index;
      vector<uint32_t>** sets;
};

#endif

And the other:

#ifndef GRAPH_HPP
#define GRAPH_HPP

#include <set>

using std::set;

class Graph
{
   public:
      Graph(uint32_t width, uint32_t length, uint32_t startN, uint32_t startP, uint32_t endN, uint32_t endP);
      ~Graph();
      int cost(uint32_t a, uint32_t b);
      void set(uint32_t a, uint32_t b, uint32_t cost);
      void print();
      bool inPath(uint32_t node);
   private:
      int32_t** adjList;
      uint32_t startN;
      uint32_t startP;
      uint32_t endN;
      uint32_t endP;
      set<uint32_t>* path;
      const uint32_t width;
      const uint32_t length;
      const uint32_t size;
      const uint32_t listWidth;
};

#endif

For some reason I get the following errors:

./Graph.hpp:23: error: ISO C++ forbids declaration of `set' with no type
./Graph.hpp:23: error: expected `;' before '<' token

I had previously run into the problem of not including ‘using std::vector’ in the ‘UnionFind.hpp’, but adding ‘using std::set’ to ‘Graph.hpp’ does not fix the problem. Also,
I’ve tried ‘using std::set< uint32_t >’, but this gives the following errors:

./Graph.hpp:6: error: a template-id may not appear in a using-declaration
./Graph.hpp:23: error: ISO C++ forbids declaration of `set' with no type
./Graph.hpp:23: error: expected `;' before '<' token

Answer 1

Change

set<uint32_t>* path;

to

std::set<uint32_t>* path;

The compiler understands set to mean the set() method you’ve declared in your class.

It’s bad style to put using ...; in a header file because you force that on everyone who includes your header file. Always use explicit namespaces in header files. Save using ...; for source files.